The present invention relates to a process for welding two members, such as metallic plate sections together, and more particularly relates to a method which employs the use of endothermic heating of a charged metal and then obtaining the necessary heat input to the edge surfaces to be welded by flowing the molten weld metal past the edge surfaces at a predetermined rate sufficient to provide a selective ratio of weld gap metal to total metal flowed to provide an efficient process with satisfactory weld quality.
In the Bergmann et al. patent, as in the present invention, the metal flow serves two purposes. One being to provide weld metal, and the other being to provide heat for melting the members to be joined. Hence, a fundamental characteristic of the present invention is that the melting of members (parent metal) to be joined is obtained by the heat input from the flow of molten weld metal. In other words, the present invention is characterized by the fact that a majority of the metal flow is for the purpose of introducing heat necessary to melt the members to be welded, rather than for the purpose of providing the weld metal in a finished weld. Hence, in the present invention, excess metal continues to flow to the weld gap and out through side dams for subsequent usage or for recycling, as desired.
In the present invention, a primary measure of the efficiency of the process is the amount of metal flowed through the weld joint during the joining cycle. The most efficient process utilizes a minimum amount of weld (filler) material consistent with satisfactory weld quality. Several parameters which influence the amount of metal circulated through the weld joint include metal temperature, spacing between the members and the input area. The temperature of the metal stream is an important element, as it directly affects the amount of metal circulated to the weld joint to achieve bonding. High melt temperatures allow faster joining rates. As the metal temperatures are lowered, more metal is required for circulation through the weld joint to achieve bonding. However, because high metal temperatures result in increased absorption of hydrogen gas, an optimum metal temperature exists for each set of joining parameters. In the invention, it has been found that minimum temperatures should be employed consistent with satisfactory joining rates, internal quality and optimum metal circulation rates. The spacing between the members influences the amount of metal flowing between the members much as in an orifice. Melting, which occurs along the weld interface, constantly enlarges the area between the members dependent on heat flow considerations and the rate of joining. Thus, after a steady state is achieved, the original spacing between the members is enlarged and a "new area" is generated by molten metal. This "new area" will control the amount of metal that passes through the gap between the members. The metal-inlet area provided by the side dams has a regulating effect on the amount of metal passed through the system since it determines the shape and size of the metal stream which flows through the weld gap and impinges along the weld interface. By controlling the inlet area, the flow rate of metal through the weld gap will be determined and the melt rate along the interface established. The velocity of the metal stream flowing along the weld interface determines the melting rate and penetration into the parent metal. In the present invention, the metal flow is preferably horizontal. Thus, the "mass" flow velocity cannot be greatly changed except by spacing between the members to be joined.
By the present invention, there is provided advantages over the prior exothermic methods which required measured amounts of exothermic reactants as noted in respect to Deppeler U.S. Pat. No. 1,795,332. In the present invention, relatively cool (as compared to Thermit temperatures) weld material is flowed through the weld gap until edge melting is initiated, whereupon, the flow is terminated to provide for weld solidification. This obviates the need to provide measured amounts of thermit materials.
The recently issued U.S. Pat. No. 3,860,062 is somewhat like Deppeler in that it discloses a portable furnace disposed above a mold for the purpose of cast welding a pair of conductors confined within the mold.